The definition of ageing can be understood as a continuous and gradual process of degradation which is relative to environment, operating conditions, structure and material, etc. of components. It has characteristic of complexity that one or several factors in combination affect a component to degrade so as to result in losing function and structure failure. Much knowledge is involved in understanding and predicting degradation (ageing) mechanism as well as mitigating and managing degradation (ageing) phenomenon. Operating experience has shown that ineffective control of the ageing degradation of the major NPP components (e.g. caused by unanticipated phenomena and by operating, maintenance, design or manufacturing errors) can jeopardize plant safety as well as plant life. At present, ageing in NPPs must be therefore effectively managed to ensure the availability of design functions throughout the plant service life. From the safety perspective, this means controlling within acceptable limits the ageing degradation and wear out of plant components important to safety so that adequate safety margins remain, i.e. integrity and functional capability in excess of normal operating requirements.

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